Drill bit

ABSTRACT

The proposed device relates to roller drill bits with air drilling capability and can be used for drilling of rocks of high hardness. The drill bit includes a body and rock-destroying elements with cutting equipment mounted on the body one inside the other by means of bearing supports, wherein the inner element is located at an angle relatively to the axis of the drill bit, and the outer element is located in the opposite direction of the axis. The device provides for an increase of the service life, high efficiency, and interchangeability due to a special design, which envisages the cutting equipment formed as replaceable jet nozzles made of hardwearing material and provided with arm insertions, preferably made of wolframite-cobalt based alloy, wherein the bearing support of each rock-destroying element is furnished with a unit adjusting the axial play value of the rock-destroying elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application of a PCTapplication PCT/UA2010/000054 filed on 2 Sep. 2010, published asWO/2011/028193, whose disclosure is incorporated herein in its entiretyby reference, which PCT application claims priority of a Ukrainianapplication UA a2009 09105 filed on 4 Sep. 2009.

FIELD OF THE INVENTION

The invention relates to a rock-destroying tool, more specifically toroller drill bits with air drilling ability. The tool can be used fordrilling rocks of a high and highest hardness by an open-cut methodduring wellbore drilling operations in the mining and metal miningindustries.

BACKGROUND OF THE INVENTION

Known roller drill bits are typically supplied with roller cuttersmounted on the leg axles by means of a retaining ball bearing and tworoller bearings, wherein both roller bearings are tapered and aretaining ball bearing is located between them. (USSR Certificate ofInventorship No 1229297, MIIK⁴ E 21 B 10/22, publ. 7 May 1986, BulletinNo 17).

Such a drill bit has the following disadvantages:

1) The widespread disadvantage of modern drill bits with tapered rollercutters, especially those that are aimed at drilling of hard rocks, isconsidered to be insufficient weight-supporting capacity of drill bitlegs. It is known that the bearing support of one section (leg) of acommon tricone roller drill bit is manufactured according to one of thefollowing arrangements: “roller-ball-roller” or “roller-sliding ball”.Even the companies that are famous world leaders in the industrymanufacture such drill bits, in which the allowed load onto the drillbit legs is equal only to 60-70% of the size, which is taken to beoptimal for the effective drilling of hard rocks. As known, the mainreason of failures of drill bits is a breakage or locking of the leg ofone of the roller cutters (it makes more than 80% of the failures). Forexample, in 2007 at the drilling of rocks in Krivoy Rog iron ore basin,the average drilling depth was 166 meters (rocks with the rigidityfactor f=16-19 according to Protodyakonov scale). With that the servicelife of hard-alloy cutting structure of a drill bit several timesexceeds the service life of the drill bit legs.

2) The bearing support of one section (leg) of a tricone drill bit withtapered roller cutters takes up approximately one-third of the loadapplied onto the drill bit. Since the axle of each leg extends at anangle of about 37-39° to the horizontal, the total load applied onto oneleg can be represented as having radial and axial components. The radialcomponent of the load applied onto the support is sustained only by theend and peripheral roller bearings and is distributed between them inthe ratio of 35 and 65% accordingly (see e.g. Drill Bits. Digest.Publication 3. Palyi P. A. Korneev K. E. “Depths”. 1971, page 446). Eachbearing of the support, in particular, the bearing race on the axle,bears the load at the limit of metal capacity of the axle, rollers androller cutters.

3) The difference in design of the legs, bearing assemblies and rollercutters of the drill bits aimed at drilling of soft rocks, rocks ofmiddle hardness and hard rocks, is so significant that the possibilityof standardization of compounding elements even for drill bits of thesame size is absolutely impossible. This is exactly the reason whyroller drill bits are expensive.

4) The axial component of the load applied onto the bearing support is avariable and negative value, which has no influence on rock destroyingcharacteristics of the drill bit. It is directed along the axis of theaxle and it makes more than 60% of the total load onto one support. Thethrust load in the traditional “roller-ball-roller” support is taken upby a double-direction retaining ball bearing. It holds the thrust loads,which are directed, both in the direction of the end bearing and in theopposite direction, i.e. in the direction of base of the axle.Double-sided loads lead to a fast wearing-out of the retaining ballbearing and cause a large axial play. It is known that when there is aplay of 3-5 mm in the support, a skew of cylindrical rollersrespectively to the bearing races occurs and the seizure of the supportstakes place, wherein a load area angle of the tapered roller bearings isdramatically lowering.

There is known a drill bit open bearing support, which has a leg with anaxle, a roller cutter, a peripheral retaining tapered roller bearingmounted close to the base of the axle, and an end tapered rollerbearing, on which the roller cutter is arranged. Herewith, theperipheral bearing is fixed on the axle and in the body of the rollercutter by means of spring rings. The end bearing is mounted on the axleso as to be freely axially (longitudinally) rotatable and it thrustsagainst the axle's shoulder through a belleville spring. In thisvariant, the support comprises a tapered roller bearing, a cylindricalroller bearing and a roller thrust bearing. (International PCTapplication No WO 2005/021923 A1, MIIK7: E 21 B 10/22. Date ofinternational publication: Mar. 10, 2005).

The above described drill bit has the following disadvantages:

1) It does not include the traditional double-direction retaining ballbearing of the support, but, instead an (imaginary) function of theretaining bearing has been centered on the peripheral tapered rollerbearing, though it is known that the latter is capable to take up onlyone-sided thrust load. The support design concept of such a drill bit(FIG. 1, 2 of the drawings attached to PCT application No WO2005/021923) includes images of typical single-row tapered rollerbearings of type 7000. Type 7000 is the principal one according to GOST333-71(R. D. Beyzelman, B. V. Tsypkin, L. Ya. Perel. Bearings. Digest.Publication b, M. “Mechanical Engineering”, 1975, p. 52-53. Furtherreferred to as the Digest). The contact angle of 7000 type bearings isα=10-17°. Also, the single-row tapered roller bearings are capable todeal only with one-sided thrust load. The allowed thrust load appliedonto the 7000 type bearings cannot exceed 70% of the allowed radial loadthat was not used. As mentioned above, the end roller bearing of thetraditional tricone roller drill bit holds about 35% of the radial loadon the support. This value balances upon the material strength limit ofthe bearing races and the bearing rollers. The additional thrust load,the value of which by 2-2.5 times exceeds the allowed radial componentof the end bearing load, may become a reason for fatal failure of theend bearing and locking of the roller cutter leg.

2) The inner ring of the end bearing of the analogue of the drill bit ismounted on the axle so as to be randomly (spontaneously) rotatable alongthe axis of the axle, which comprises a cylindrical shoulder from theside of the peripheral bearing. The belleville spring being providedbetween the shoulder and the inner ring of the end bearing assumes toensure the preliminary axial tension and the power closure of theelements of both roller bearings, which allegedly eliminates thepossibility of axial play (backlash) in the support.

However, kinetostatic analysis over the interaction of components of thesupport of the foregoing drill bit has shown the following:

a) When roller cutter body is immovable by convention (the body of theroller cutter is supported by an absolutely rigid surface), the radialcomponent of the load applied onto the axle (leg) is distributed betweentwo roller bearings (FIG. 1 of PCT application No WO 2005/021923).Through the cylindrical shoulder on the axle, the thrust load comes atfull on the belleville spring and deforms it deeply. Since all theelements of the end roller bearing are already closed between each otherand with the roller cutter body, the only available direction for themovements in the support is longitudinal rotation of the axle throughthe inner ring hole of the end bearing in the direction of the top ofthe roller cutter. In this respect, the inner ring of the peripheraltapered roller bearing together with the tapered rollers, the retainerand the axle will move in the direction of the roller cutter's top. Theimaginary retaining peripheral roller bearing opens up consequently,since the rollers located above the axis of the axle are not capable anymore to come in contact with the outer ring. Therewith the radial playexceeds the allowed specified value by several times (Digest, p. 168,table 14). As a result, the load area angle of the bearing isdramatically lowering (down to a value of 60-90° instead of an optimalvalue of 170-180°), and the pressure applied to the elements of thebearing may exceed marginally the allowed value.

b) When the axle is immovable by convention, the axial component of theload onto the roller cutter is directed along the axis of the axle inthe direction of its base. Through the roller cutter's body, the outerring, rollers and the inner ring of the end bearing, the thrust loadcomes at full on the belleville spring and deforms it deeply. With that,the body of the roller cutter, the end bearing, the belleville spring,and the outer ring of the (imaginary) retaining peripheral taperedroller bearing will move in the direction of the axle base by a valueequal to the size of deformation of the belleville spring. The(imaginary retaining) peripheral roller bearing opens up again, itsradial play grows quickly and the load area angle of the bearing lowersdramatically. Taking into account the fact that when operating the loadsapplied onto the supports of the roller cutters of the drill bit aredrilling and repeating in any case, the additional axial and radialvibrations in the supports will have an extremely negative influence onthe service life of the drill bit. That's exactly why the radial andaxial plays in any support are aimed to be minimal and strictly limited.The main disadvantage of the support design of the aforesaid drill bitis that the imaginary peripheral retaining tapered roller bearing inreality doesn't have any influence on the value of the axial play inthis support.

3) Another type of the bearing support of another drill bit (FIG. 2 ofPCT application No WO 2005/021923) known in the related art, comprisingone single-row tapered roller bearing, one roller bearing withcylindrical rollers, and one thrust ball bearing, doesn't comply withthe simple rules of use of tapered and thrust bearings, in particular:

a) Single-row tapered roller bearings should build at least one pair inthe support (Digest, p. 53 paragraph 2; p. 169, FIG. 3-b, 3-d).

b) Thrust bearings have some peculiarities as to how their thrust ringsshould be mounted on the shaft and in the body. For example, it isrequired to mount one thrust ring on the shaft firmly, with the standardlevel of tightness, while the other thrust ring should be assembled withthe standard level of looseness, which is equal to 0.2-0.4 mm. Thelooseness is ensured in that the inner diameter of the second thrustring is wider by 0.2-0.4 mm than the shaft diameter. The diameter of thegroove in the body dedicated to mount the second ring should be by 0.5-1mm wider than the outer diameter of the thrust bearing. On the top ofthat GOST contains the compulsory requirements as to minimal allowedwidth of the thrust surface separately from the pair “ring-shaft” andthe pair “ring-body” (Digest, p. 520-523 table 19). The design of theforegoing drill bit has ignored all these requirements (see drawings ofPCT No WO 2005/021923, FIG. 2). For instance, one thrust ring mounted onthe axle with the radial play (rotatable mounting) and the other ringand rolling elements mounted together with the retainer are arrangedoutside the axle. Having ignored the required width of the thrustsurfaces for the rings of the thrust ball bearings, the design has usedthe belleville spring end (linear contact) as the thrust surface of thethrust ring.

c) The imaginary peripheral retaining tapered roller bearing is arrangedin the body of the roller cutter by means of a threaded bush, though thethreaded couplings are not aimed at sustaining the dynamical radialloads. For this purpose, if required, cylindrical liners, cups, etc. areused with the radial tightness of the cylindrical joint surfaces, whichliners, cups, etc. are to be firmly mounted together with the bearing inthe main body (for example: Digest, p. 380 FIG. 2 and p. 381 FIG. 3).

The supports represented on FIGS. 1 and 2 (PCT application No WO2005/021923) don't meet the simple requirements as to the design ofdrill bit supports, since no principle elements ensuring the limitationof the axial play value are provided.

The closest prior art device, herein called a prototype, is consideredto be a drill bit comprising a body and rock-destroying elements with anequipment, wherein the rock-destroying elements are mounted on the bodyone inside the other by means of bearing supports, wherein the one,inwardly assembled, is located at an angle relatively to the axis of thedrill bit, and the outer one is located in the opposite direction inrelation to the axis of the drill bit (USSR Certificate of InventorshipNo 512282, MIIK2: E 21 B 9/08, publ. 30 Apr. 1976, Bulletin No 16).

The prototype drill bit has the following disadvantages:

1) The bearing supports of the drill bit are introduced asall-in-one-piece, and in the same way as they are presented in triconedrill bits, they are furnished with retaining ball bearings, which aremounted in the supports by means of access holes and ball plugs. Suchretaining bearings don't provide any possibility for a preliminary orcurrent control over the value of axial play.

2) The techniques of the production of the bearing races on the body inthe cavity of the roller cutters are very complicated andtime-consuming, just like the techniques the tricone drill bits arebased on.

3) Like in other drill bits, the duration of the service life of themain components of the drill bit prototype (i.e. the body, bearingsupports, and roller cutter equipment) differs greatly. For instance, atthe test operations of the drill bit samples from the trial batch it wasdetermined that for the first time ever the service life of the bearingsupports has several times overgrown the service life of thewolframite-cobalt rock-destroying elements. This became possible becausethe angle of the bearing load zone in the support of the drill bitprototype is equal to 360°, but it makes not more than 160-175° in thetricone drill bits right after the run-in test.

When wearing-out of the operating surfaces of the rock-destroyingelements of the drill-bit prototype provided with hard-alloy cutters wasalready 100%, the wearing-out of the drill bit body was not more than25% and the wearing-out of the bearing supports was 35%. Such drill bitsthat are worn out in half, are not subject to repairing as the design ofthe drill bit prototype doesn't provide the possibility of changing orrecovering the components that are worn-out.

BRIEF DESCRIPTION OF THE INVENTION

Therefore, the goal of the present invention is to sufficiently increasethe service life of the drill bits, their efficiency andinterchangeability.

The aforesaid goal is achieved due to the inventive design of the drillbit. Accordingly, the drill bit comprises: a body and rock-destroyingelements with cutting equipment, said rock-destroying elements includean inner element and an outer element mounted on the body one inside theother by means of bearing supports, wherein the inner element is locatedat an angle relatively to the axis of the drill bit, and the outerelement is located in the opposite direction of the axis of the drillbit, and, in accordance with the invention, the cutting equipment isformed as replaceable jet nozzles (matrices) made of a predeterminedhardwearing material and provided with arm insertions made of apredetermined firm material, wherein the bearing support of eachrock-destroying element is furnished with an adjustment unit to adjustthe axial play value (or preliminary tightness).

The inventive design of the drill bit offers the following advantages:

the use of replaceable jet nozzles (matrices) that are quickly removableand exposed to wear allows maintaining reliable operation of the drillbit until the complete wearing out of all elements (body, roller cuttersand bearing supports) takes place;the use of replaceable jet nozzles, i.e. the removable equipment of theroller cutters, which, if desired, might be different in quantity, sizeand shape of hard-alloy cutters, including those that arediamond-tipped, ensures standardization of the drill bit. With thatbeing said the drill bits of one definite size, aimed at drilling ofsoft rocks, rocks of middle hardness, hard rocks and rocks of thehighest hardness, might be different only in material and geometricalshape of the cutters of the replaceable jet nozzles equipment.replaceable jet nozzles allow using cheaper material for the body of thedrill bit and body parts of the rock-destroying elements, wherein thereplaceable jet nozzles can be made of high-hardness steel and alloyshaving special properties of hardness, abrasion resistance, etc.;equipment of rock-destroying elements resistant to wearing out togetherwith the solid bearing supports that are taking up only useful one-sidedthrust load and having the angle of the load of 3600, allow increasingthe operational life of the drill bit by 3-5 times, wherein only costsfor manufacturing of the spare units of the equipment are required.the units for adjusting the axial play or preliminary tightness in thesupports of the rock-destroying elements allow avoiding the world'scommon practices of selective grouping of rolling elements depending onthe actual diameter of the bearing races on the axle and in the cavityof the roller cutters, which are unique for each section of the drillbit.as a result of the aforesaid, it is possible to standardize themanufacturing of some parts of the drill bit: legs, roller cutters,bearings or rolling elements, and retainers. Due to these measures, themanufacturing and assembling of the drill bits are sufficientlysimplified and cheapened.

BRIEF DESCRIPTION OF THE DRAWINGS

Three possible variants (preferred embodiments) to manufacture the drillbit are described by means of accompanying drawings, i.e.:

FIG. 1 shows a front sectional plane view of the drill bit withseparable ball bearings;

FIG. 2 shows a front sectional plane view of the drill bit withseparable roller bearings;

FIG. 3 shows a front sectional plane view of the drill bit withseparable supports comprising typical bearings provided with the outerand inner rings, rolling elements and retainers;

FIG. 4 shows a photographic view of the trial model of the drill bit,i.e. a variant with the central nozzle.

PREFERRED EMBODIMENTS OF THE INVENTION

While the invention may be susceptible to embodiment in different forms,there are described in detail herein below, specific embodiments of thepresent invention, with the understanding that the present disclosure isto be considered an exemplification of the principles of the invention,and is not intended to limit the invention to that as illustrated anddescribed herein.

In a preferred embodiment, the inventive drill bit (shown on FIG. 1)comprises a body 1, with scavenge channels 2 and rock-destroyingelements: an inner rock-destroying element 3 and an outerrock-destroying element 4, which are made in the form of front rollercutters. The rock-destroying elements are mounted on the body by meansof separable bearing assemblies (supports) 5 and 6, which include thrustball bearings. Being exposed to wear, the operating part of therock-destroying element is provided with replaceable jet nozzles 7 and8. The jet nozzles are made of hardwearing material and provided withcutters 9 made of firm material, for example, of wolframite-cobalt basedalloy or an extra-hard composite formed on the basis of synthetic andnatural diamonds. The jet nozzles are fixed on the ends of therock-destroying elements with conventional fasten means, for example,with screws.

The upper thrust ball bearing of the support of the rock-destroyingelement 3 is provided with a retaining ring 10 and an adjusting unit 11to adjust the axial play value in the support realized, for example, inthe form of an end plate and a bolt. In its turn, the ball bearingsupport 5 of the outer rock-destroying element 4 is provided with aretaining ring 12 and a threaded-type cap 13 for adjusting the axialplay value in the support. The cap has a seal ring.

In another preferred embodiment, the inventive drill bit, shown furtheron FIG. 2, comprises a body with scavenge channels 2 and rock-destroyingelements 3 and 4, mounted on the body by means of bearing supports 14and 15, which include tapered roller bearings with a retainer. Thebearing supports 14, 15 are furnished with units 16 and 17 to adjust theaxial play value. The unit 17 makes the supports replaceable.

Yet, in another preferred embodiment, the inventive drill bit (shown onFIG. 3) comprises a body 1 with scavenge channels 2 and rock-destroyingelements 3 and 4, mounted on the body by means of bearing supports 18and 19, which include typical bearings: radial bearings or tapered ballbearings, tapered roller bearings, etc. provided with the outer andinner rings, rolling elements and retainers. For example, ball bearingsof the following types can be utilized: 0000 GOST 8338-93; 60000 and80000 GOST 7242-85; 1000 GOST 5720-75; 3000 GOST 8545-78; 6000 GOST831-90; 7000 GOST 333-94; 8000 GOST 6874-82, etc.

The rock-destroying elements are provided with the replaceable jetnozzles made of hardwearing material. The operating parts of the jetnozzles are equipped with cutters 9 made of a suitable known firmmaterial, for example, of wolframite-cobalt based alloy or an extra-hardcomposite formed on the basis of synthetic and natural diamonds. Theends of the cutters can be diamond-tipped.

The inventive drill bit operates as follows. The body of the drill bitis connected to a drillpipe of the drilling machine. The rotating drillbit with the axial play being set is brought to the downhole.Simultaneously the air is delivered under the pressure through thescavenge channels 2. As far as the cutters 9 are deepened in the surfaceof the downhole, the rock-destroying elements come in contact with therock and roll over the downhole due to rotation of the body 1 of thedrill bit. The zones of contacts of the rock-destroying elements arelocated on the opposite sides relatively to the axis of the downhole,which eliminates the possibility of radial vibrations of the drill bitrelatively to the axis of the well. The movement path of each cutter 9of the jet nozzles 7 and 8 can be described as a waveform type. Herewithcutters 9 cut the local parts of the downhole in a sequential order, bydestroying and grinding a predetermined layer of the rock. Currents ofthe compressed air blow away the drilling mud from the downhole surfaceand deliver it onto the ground surface within an annular space. The coneshape of the outer rock-destroying element minimizes the possibility ofits contact with the hole walls. Thanks to that, the working torque ofthe motor on the shaft is reduced and heating of the drill bit parts isminimal.

The bench tests and tests in natural conditions of the trial models ofthe drill bits (for example, shown on FIG. 4) proved a high efficiencyof these drill bits comparatively to the ones of traditional triconeroller drill bits, in particular, there have been observed:

an increase of the mechanical speed of the drilling by 2-2.5 timesthanks to the possibility to grow the load on the drill bit;a decrease of the value of the required torque of the motor by 2-3times;enhancement of the service life of the drill bit bearing supports by10-45 times as a result of increasing the angle of the bearing load zonein the support up to 360°;an increase of the service life of hard-alloy cutting equipment of therock-destroying elements by 3-5 times due to changing their movementpaths and angles of cutters entering the rock;an increase of the service life of the drill bit itself by 4-5 timesthanks to introduction of replaceable assemblies of the equipment.

1. A drill bit having an axis, and comprising: a body androck-destroying elements supplied with cutting equipment, saidrock-destroying elements include an inner element and an outer elementmounted on the body one inside the other by means of bearing supports,said inner element is located at an angle relatively to the axis, andsaid outer element is located at the opposite direction of the axis;wherein the cutting equipment is formed as replaceable jet nozzles madeof a predetermined hardwearing material and provided with arm insertionsmade of a predetermined firm material, wherein each said bearing supportis furnished with a means for adjusting an axial play value of saidrock-destroying elements.